Aqueous silica slurry compositions for use in shallow trench isolation and methods of using them

ABSTRACT

The present invention provides aqueous CMP polishing compositions comprising a from 0.5 to 30 wt. %, based on the total weight of the composition of a dispersion of a plurality of elongated, bent or nodular silica particles which contain a cationic nitrogen atom, and from 0.001 to 0.5 wt. %, preferably from 10 to 500 ppm, of a cationic copolymer of a diallylamine salt having a cationic amine group, such as a diallylammonium halide, or a diallylalkylamine salt having a cationic amine group, such as a diallylalkylammonium salt, or mixtures of the copolymers, wherein the compositions have a pH of from 1 to 4.5. Preferably, the cationic copolymer of a diallylamine salt having a cationic amine group comprises a copolymer of diallylammonium chloride and sulfur dioxide and the copolymer of the diallylalkylamine salt having a cationic amine group comprises a copolymer of diallylmonomethylammonium halide, e.g. chloride, and sulfur dioxide. The slurry compositions demonstrate good oxide selectivity in the CMP polishing of pattern wafers having nitride and silicon patterns.

The present invention relates to aqueous chemical mechanicalplanarization (CMP) polishing compositions comprising one or moredispersions of a plurality of spherical colloidal silica particles, ofelongated, bent, or nodular silica particles, or their mixtures whichcontain a cationic nitrogen atom, and a copolymer of a diallylamine salthaving a cationic amine group, such as diallylammonium chloride andsulfur dioxide or a copolymer of a diallylalkylamine salt having acationic amine group, such as diallylmonomethylammonium chloride andsulfur dioxide wherein the compositions have a pH of from 1 to 4.5.

In front-end-of-line (FEOL) semiconductor processing, shallow trenchisolation (STI) is critical to the formation of gates in integratedcircuit fabrication, such as prior to formation of the transistors. InSTI, a dielectric such as tetraethyl orthosilicate (TEOS) or silicondioxide is deposited in excess in openings formed in the silicon wafer,for example, a trench or isolation area which is isolated from theremainder of the integrated circuit by silicon nitride (SiN) barrier. ACMP process is then used to remove the excess dielectric, resulting in astructure in which a predetermined pattern of the dielectric is inlaidin the silicon wafer. CMP for STI requires the removal and planarizationof the silicon dioxide overburden from the isolation areas, therebyresulting in a coplanar surface with the silicon dioxide-filledtrenches. In STI, the silicon nitride film surfaces must be cleared ofthe silicon dioxide or oxide to allow subsequent removal of the nitridehard mask in downstream processing. An acceptable oxide:nitride removalrate ratio is necessary to prevent damage to the underlying Si activeareas and provide an overpolish margin to ensure all pattern densitiesare cleared of the oxide. Further, dishing of the oxide in any trenchmust be avoided to prevent low threshold voltage leaks in finishedgates.

Presently, users of aqueous chemical, mechanical planarization polishing(CMP polishing) compositions used with CMP polishing pads to polishsubstrates wish to avoid the use of ceria containing CMP polishingcompositions. Ceria slurries show high selectivity for silicon dioxideover silicon nitride and avoid removal of oxide in the trench area uponexposure of silicon nitride, but are costly, have issues with removalrate (RR) and process stability, and are prone to causing defects duringpolishing.

Silica slurry formulations offer lower cost, defect-free solutions, but,to date, have suffered from unsatisfactory oxide dishing control andinadequate oxide:nitride selectivity for use in STI applications.

U.S. Pat. No. 9,303,188 B2, to Grumbine et al. discloses a chemicalmechanical polishing composition for polishing a substrate having atungsten layer, the composition comprising a water based liquid carrier,a cationically charged colloidal silica abrasive and a polycationicamine compound in solution in the liquid carrier. The compositions mayinclude an amine based polymer chosen from polyamines and polymerscontaining amine functional groups, such as diallylammonium chloride.The compositions do not exhibit acceptable oxide dishing control andinadequate oxide:nitride selectivity for use in STI applications.

The present inventors have endeavored to solve the problem of providingaqueous silica slurries which enable acceptable oxide dishing controland oxide:nitride selectivity for use in STI applications, as well asmethods for using the slurries.

STATEMENT OF THE INVENTION

1. In accordance with the present invention, aqueous chemical mechanicalplanarization polishing (CMP polishing) compositions comprise adispersion of a plurality of elongated, bent or nodular colloidal silicaparticles which contain a cationic nitrogen atom or a mixture thereofwith a dispersion of a plurality of spherical colloidal silicaparticles, for example, those having for the average particle an aspectratio of the longest dimension of the particle to its diameter which isperpendicular to the longest dimension of from 1.8:1 to 3:1, and from0.001 to 0.5 wt. % or, preferably, from 10 to 500 ppm of a cationiccopolymer of a diallylamine salt having a cationic amine group, such asa diallylammonium salt, preferably, a halide salt, such as a copolymerof diallylammonium halide and sulfur dioxide, or a copolymer ofdiallylalkylamine salt having a cationic amine group, such as adiallylalkylammonium halide, preferably, diallylmonomethylammonium salt,such as, preferably, a halide salt, such as, preferably,diallylmonomethylammonium chloride, and sulfur dioxide, or mixturesthereof, wherein the compositions have a pH of from 1 to 4.5 or,preferably, from 2.5 to 4.3, and, further wherein, the amount of thedispersion of the elongated, bent or nodular silica particles, rangesfrom 0.5 to 30 wt. %, or, preferably, from 1 to 25 wt. %, or, morepreferably, from 1 to 20 wt. %, as solids, based on the total weight ofthe composition.

2. In accordance with the aqueous CMP polishing compositions as setforth in item 1, above, compositions comprise a mixture of a dispersionof a plurality of elongated, bent or nodular colloidal silica particleswhich contain a cationic nitrogen atom with a dispersion of a pluralityof spherical colloidal silica particles, wherein the amount of thedispersion of the elongated, bent or nodular colloidal silica particlesranges from 80 to 99.9 wt. %, or, preferably, from 95 to 99.9 wt. %,based on the total solids weight of the colloidal silica particles inthe compositions.

3. In accordance with the aqueous CMP polishing compositions as setforth in any one of items 1 or 2, above, wherein the weight averageparticle sizes (CPS) of the silica particles in the dispersion of silicaparticles or a weighted average of such particle sizes of a mixturethereof ranges from 10 nm to 200 nm, or, preferably, from 25 nm to 80nm.

4. In accordance with the aqueous CMP polishing compositions as setforth in any one of items 1, 2 or 3, above, wherein the cationiccopolymer of the diallylammonium salt, and sulfur dioxide comprises acopolymer of 45 to 55 mole % or, preferably, from 48 to 52 mole % of thediallylamine salt having a cationic amine group, such as adiallylammonium salt, such as, preferably, a halide salt, and from 45 to55 mole % or, preferably, from 48 to 52 mole % of the sulfur dioxide, orthe cationic copolymer of a diallylalkylamine salt having a cationicamine group, such as a diallylalkylammonium salt, or adiallylalkylammonium halide, preferably, diallylmonomethylammonium salt,such as, preferably, a halide salt, such as, preferably,diallylmonomethylammonium chloride, and sulfur dioxide comprises acopolymer of 45 to 55 mole % or, preferably, from 48 to 52 mole % of thediallylmonomethylammonium salt and from 45 to 55 mole % or, preferably,from 48 to 52 mole % of the sulfur dioxide.

5. In accordance with the aqueous CMP polishing compositions as setforth in any one of items 1, 2, 3, or 4, above, wherein the cationiccopolymer of the diallylamine salt having a cationic amine group,preferably, a halide salt, and sulfur dioxide or the cationic copolymerof diallylalkylamine salt having a cationic amine group, preferably, ahalide salt, or, more preferably, an ammonium halide, and sulfurdioxide, or the weighted average of a mixture thereof, has a weightaverage molecular weight of from 1,000 to 15,000 or, preferably, from2,000 to 12,000.

6. In accordance with another aspect of the present invention, methodsof using the aqueous CMP polishing compositions comprise polishing asubstrate with a CMP polishing pad and an aqueous CMP polishingcomposition as set forth in any one of items 1 to 5, above.

7. In accordance with the methods of the present invention as set forthin item 6, above, wherein the substrate comprises both silicon dioxideor tetraethyl orthosilicate (TEOS) and silicon nitrides, as SiN or Si₃N₄or their mixtures, and the polishing results in an oxide:nitride removalrate ratio of at least 3:1, for example, from 3:1 to 25:1 or,preferably, from 8:1 to 18:1, for example, at least 8:1.

8. In accordance with the methods of the present invention for polishinga substrate as in any one of items 6 or 7, above, wherein the polishingdownforce ranges from 6.9 kPa (1 psi) to 41.5 kPa (6 psi) or,preferably, from 12 kPa (1.8 psi) to 36 kPa (5.2 psi).

9. In accordance with the methods of the present invention for polishinga substrate as in any one of items 6, 7 or 8, above, wherein the CMPpolishing composition comprises a total of from 0.5 to 5 wt. %, or,preferably, from 1 to 3 wt. %, total solids content of the dispersion ofthe elongated, bent or nodular colloidal silica particles, sphericalcolloidal silica particles, or their mixture. The CMP polishingcompositions may be stored and shipped as a concentrate and then dilutedwith water at the time of polishing the substrate.

Unless otherwise indicated, conditions of temperature and pressure areambient temperature and standard pressure. All ranges recited areinclusive and combinable.

Unless otherwise indicated, any term containing parentheses refers,alternatively, to the whole term as if no parentheses were present andthe term without them, and combinations of each alternative.

All ranges are inclusive and combinable. For example, the term “a rangeof 50 to 3000 cPs, or 100 or more cPs” would include each of 50 to 100cPs, 50 to 3000 cPs and 100 to 3000 cPs.

As used herein, the term “ASTM” refers to publications of ASTMInternational, West Conshohocken, Pa.

As used herein, the term “colloidally stable” means that a givencomposition does not gel or precipitate, and remains clear upon visibleinspection after a given time and at a given temperature.

As used herein, the term “hard base” refers to metal hydroxides,including alkali(ne earth) metal hydroxides, such as NaOH, KOH, orCa(OH)₂.

As used herein, the term “ISO” refers to publications of theInternational Organization for Standardization, Geneva, CH.

As used herein, the term “Particle size (CPS)” means the weight averageparticle size of a composition as determined by a CPS Instruments (TheNetherlands) disc centrifuge system. The particles are separated by sizeusing centrifugal forces in a solvent and quantified using optical lightscattering.

As used herein, the term “cationic amine group” includes a salt of aminehydroxide group that forms in aqueous media.

As used herein, the term “Shore D hardness” is the 2 second hardness ofa given material as measured according to ASTM D2240-15 (2015),“Standard Test Method for Rubber Property, Durometer Hardness”. Hardnesswas measured on a Rex Hybrid hardness tester (Rex Gauge Company, Inc.,Buffalo Grove, Ill.), equipped with a D probe. Six samples were stackedand shuffled for each hardness measurement; and each pad tested wasconditioned by placing it in 50 percent relative humidity for five daysat 23° C. before testing and using methodology outlined in ASTM D2240-15(2015) to improve the repeatability of the hardness tests. In thepresent invention, the Shore D hardness of the polyurethane reactionproduct of the polishing layer or pad includes the Shore D hardness ofthat reaction product.

As used herein, the term “silica particle solids” or “silica solids”means, for a given composition, the total amount of spherical silicaparticles, plus the total amount of elongated, bent or nodular silicaparticles, including anything with which any of those particles aretreated.

As used herein, the term “solids” means any material other than water orammonia that does not volatilize in use conditions, no matter what itsphysical state. Thus, liquid silanes or additives that do not volatilizein use conditions are considered “solids”.

As used herein, the term “strong acid” refers to protic acids having apK_(a) of 2 or less, such as inorganic acids like sulfuric or nitricacid.

As used herein, the term “use conditions” means the temperature andpressure at which a given composition is used, including increases intemperature and pressure during or as a result of use.

As used herein, the term “weight fraction silica” means the total wt. %of silica, based on the total weight of the composition/100%. Thus, 30wt. % silica equates to a weight fraction of 0.3.

As used herein, the term “weighted average” means the average of two ormore measures (e.g. average particle size or molecular weight) fromdifferent compositions (e.g. a dispersion of spherical colloidal silicaparticles and a dispersion of elongated colloidal silica particles)resulting from multiplying each by its solids weight fraction whereinthe total solids weight fraction adds up to unity (1.00).

As used herein, the term “wt. %” stands for weight percent.

As used herein, the term “elongated, bent or nodular colloidal silicaparticles” refers to silica particles having, in the average particle,an aspect ratio of longest dimension to the diameter which isperpendicular to the longest dimension of from 1.8:1 to 3:1 asdetermined by any methods known to the ordinary skilled artisan, such astransmission electron microscopy (TEM) or as reported by a manufacturerof the dispersion of particles.

The present inventors have surprisingly found that an aqueous CMPpolishing composition of a dispersion of elongated, bent or nodularcolloidal silica particles having a cationic charge and up to 0.5 wt. %,based on the total weight of the composition, of a cationic copolymer ofa diallylamine salt having a cationic amine group, such as adiallylammonium salt, or a diallylalkylamine salt having a cationicamine group, such as a diallylalkylammonium salt, for example, adiallylalkylammonium halide, preferably, a diallylmonomethylammoniumsalt and sulfur dioxide is particularly well-suited for planarizing orpolishing a substrate, such as a silicon wafer that has undergoneshallow trench isolation (STI) processing. Pressure responsecharacterizations on blanket silicon wafers revealed that these slurriespolish silicon oxide in a non-Prestonian manner: Oxide removal rate isnegligible at a low down-force and increases with increasing down-force,at pressures higher than a “turn on” pressure. The x-intercept of such anon-Prestonian oxide RR (y axis) vs. down-force (x axis) curve isnon-zero. The aqueous CMP polishing compositions of the presentinvention enable the CMP polishing of silicon dioxide with asatisfactory removal rate, and provide acceptable selectivity forsilicon oxides over silicon nitrides both on blanket and pattern wafers.Most significantly, the compositions enable improved trench oxide lossand dishing over time compared to other silica slurries.

In accordance with the present invention, suitable colloidal silicacompositions may comprise a dispersion of silica made by conventionalsol gel polymerization or by the suspension polymerization of waterglass so as to produce a plurality of elongated, bent or nodular silicaparticles in a distribution or mixture that may include spherical silicaparticles.

Suitable dispersions of elongated, bent or nodular colloidal silicaparticles are made from suspension polymerization by hydrolyticcondensation of silanols formed in a known manner from precursors liketetraethoxysilane (TEOS) or tetramethoxysilane (TMOS). Processes formaking the elongated, bent or nodular silica particles are known and canbe found, for example, U.S. Pat. No. 8,529,787 to Higuchi et al. Thehydrolytic condensation comprises reacting the precursors in aqueoussuspension in the presence of a basic catalyst, such as an alkylammoniumhydroxides, alkoxyalkyl amines, such as ethoxypropylamine (EOPA),alkylamines or KOH, preferably, tetramethylammonium hydroxide; thehydrolytic condensation process may incorporate one or more cationicnitrogen atoms into the elongated, bent or nodular silica particles.Preferably, the elongated, bent or nodular silica particles are cationicat a pH of 4 or below.

Suitable dispersions of bent or nodular colloidal silica particles areavailable from Fuso Chemical Co., Ltd., Osaka, JP (Fuso) under thetradenames HL-2, HL-3, HL-4, PL-2, PL-3 or BS-2 and BS-3 slurries. TheHL and BS series particles from Fuso contain one or more nitrogen atomswhich impart a cationic charge at pH 4 or below.

To insure colloidal stability of the aqueous CMP polishing compositionsof the present invention, the compositions have a pH ranging from 1 to4.5 or, preferably, from 2.5 to 4. The compositions tend to lose theirstability above the desired pH range. The cationic diallylamine salt ordiallylalkylamine salt having a cationic amine group and sulfur dioxidecopolymer of the present invention aids in selectivity and in preventingdishing in polishing. Amounts of the cationic copolymer range up to 0.5wt. %, based on the total weight of the composition. Too much of thecationic copolymer can passivate the dielectric or silica surface of thesubstrates.

The cationic copolymer of the present invention may be made by additionpolymerization in the presence of or in the absence of an acid, such ashydrochloric acid or glycolic acid and a radical polymerizationinitiator, such as ammonium persulfate, in a polar solvent such aswater. Such polymerization methods are detailed, for example, in U.S.Pat. No. 9,006,383 B2 to Yusuke et al.

The aqueous CMP polishing compositions of the present invention mayinclude pH adjusters, such as inorganic acids, for example, nitric acid,or organic acids, such as citric acid.

The aqueous CMP polishing compositions of the present invention maycomprise other cationic additives, such as polyamines, in amounts of upto 1 wt. %, based on total solids.

Suitable additives may also include, for example, quaternary ammoniumcompounds and diquaternary ammonium compounds, such as, for example,N,N,N,N′,N′,N′-hexabutyl-1,4-butanediammonium dihydroxide, 98 wt. %(Sachem, Austin, Tex.); and cationic aminosilanes, such as, for example,N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 98% (Gelest Inc.,Morrisville, Pa.) or N,N-diethylaminomethyl)triethoxysilane, 98%,(Gelest Inc.).

Preferably, the aqueous CMP polishing compositions consist essentiallyof the inventive copolymer of the diallylamine salt or thediallylalkylamine salt having a cationic amine group and sulfur dioxideand the cationic abrasive and do not include materials which wouldfurther interact with the abrasive components or the copolymer. Suchcompositions preferably do not include diquaternary ammonium compoundsthat interacts with silica; and they do not include anionic compoundsand nonionic surfactants that interact with the copolymer. The aqueousCMP polishing compositions may be diluted with water or with anotherliquid miscible with water.

Desirably, the CMP polishing of the present invention is carried out inSTI processing with the CMP polishing composition of the invention,preferably such that the silicon nitride is not substantially removedand the silicon dioxide is adequately planarized without excessiveerosion or dishing of dielectric or silicon dioxide within the trenches.

In use, STI processing of a wafer substrate involves providing a siliconsubstrate on which is deposited a layer of silicon nitride. Followingphotolithography, trenches are etched onto the substrate comprising anoverlying layer of silicon nitride, and an excess of dielectric, forexample, silicon dioxide, is deposited thereon. The substrate is thensubjected to planarization until the surface layer of silicon nitride isexposed but not substantially removed, such that the dielectric orsilicon oxide remaining in the trenches is approximately level with theedges of the silicon nitride.

EXAMPLES

The following examples illustrate the various features of the presentinvention.

In the Examples that follow, unless otherwise indicated, conditions oftemperature and pressure are ambient or room temperature and standardpressure.

The following materials, including those listed in Table A, below, wereused in the Examples that follow:

TABLE A Silica and Other Abrasive Particles Particle Concen- Aqueoussize Raw tration Silica (CPS, Mate- (wt. % Slurry Source pH³ nm)Morphology rials solids) Slurry A HL-3 ™^(,1) 7.8 55 Elongated, TMOS 20cationic² particle Slurry B Ceria (see separate listing, below) ¹FusoChemical, Osaka, JP; ²Charge determined at pH of 3.0 and cationicparticles formed with TMOS and an amine containing alkaline catalyst,such as tetramethylammonium hydroxide; ³pH as delivered from source.

Copolymer 1 is a 1:1 copolymer of diallylammonium chloride and sulfurdioxide, having a weight average molecular weight (MW) (GPC usingpolyethylene glycol standards) of 5,000 as reported by manufacturer(PAS-92A, Nitto Boseke Co. Ltd, Fukushima, JP);

Copolymer 2 is a 1:1 copolymer of diallylmonomethylammonium chloride andsulfur dioxide, having a weight average molecular weight (MW) (GPC usingpolyethylene glycol standards) of 3,000 as reported by manufacturer(PAS-2201CL, Nitto Boseke Co. Ltd, Fukushima, JP);

Slurry B: Ceria slurry, pH 5.2, polyacrylic acid dispersant, 0.75 wt. %ceria solids undiluted, 1:3 dilution as used.

Slurry A is positively charged below pH 4.5.

The various silica particles used in the Examples are listed in Table A,above.

The following abbreviations were used in the Examples that follow:

POU: Point of use; RR: Removal rate;

The following test methods were used in the Examples that follow:

pH at POU:

The pH at point of use (pH at POU) was that measured during removal ratetesting after dilution of the indicated concentrate compositions withwater to the indicated solids content.

Removal Rate:

In a removal rate test, a Mirra™ (200 mm) polishing machine or “MirraRR” (Applied Materials, Santa Clara, Calif.) polishing device with anIC1010™ σr other indicated CMP polishing pad (The Dow Chemical Company,Midland, Mich. (Dow)) was used to polish an STI pattern wafer substratehaving a specified feature % (which corresponds to the area of active orhigh areas in the wafer relative to the total area thereof) with an MITmask (SKW-3 wafers, SKW, Inc. Santa Clara, Calif.) using the CMPpolishing compositions defined in Table 1, below, at a 20.7 kPa (3 psi)down-force, slurry flow rate of 150 mL/min, a 93 rpm platen speed and an87 rpm carrier speed. During polishing, the pad was conditioned with aKinik™ AD3CS-211250-1FN conditioning disk (Kinik Company, Taiwan) at a3.17 kg (7 lbf) pressure, using 100% in situ conditioning.

Multi-Step CMP Polishing—P1 (First Step) and P2 (Subsequent Steps):

CMP polishing was conducted such that, in the first step or P1 process,the overburden high density plasma oxide (HDP) film was removed. Thefilm was polished using a VP6000™ polyurethane CMP polishing pad (Dow,Shore D (2 second) hardness: 53) and Slurry E and by applying apolishing down-force of 20.7 kPa (3 psi) and platen speed of 93 rpm. P1polishing was stopped when complete planarization was achieved on the50% pattern density (PD) feature on the middle die of the wafer. At thispoint, ˜500 Å of HDP film remained on the 50% feature. On the smallerfeatures, such as the 10% and 20% PD features, however, the HDP film wascompletely removed and the underlying nitride film was exposed. Featureswith >50% PD still had significant dielectric film over the nitridefilm. Before moving to P2, the patterned wafer was cleaned using SP100cleaning chemistry (TMAH containing) on a OnTrak DSS-200 Synergy™ tool(Lam Research, Fremont, Calif.) to remove ceria particles from thewafer. P2 polishing was performed using an IC™ polyurethane polishingpad (Dow, Shore D (2 second) hardness: 70) with 1010™ groove design(Dow) and the indicated slurry composition, using a polishing down-forceof 20.7 kPa (3 psi) and a platen speed of 93 rpm. For the 50% patterndensity feature, the polishing endpoint was defined as the time at whichthe HDP was cleared and the nitride film was exposed. Trench oxide losswas monitored on the 50% pattern density feature for each step-polishingevent. The HDP oxide removal on the 100% pattern density feature wasalso measured. Overpolish is defined as the amount of HDP film removedon the 100% feature after silicon nitride was exposed on the 50% patterndensity feature. Selectivity was calculated as the ratio of siliconnitride removal rate to the ratio of HDP oxide removal rate on the 100%feature. All dielectric film thicknesses and removal rates weredetermined by measuring the film thickness before and after polishingusing a KLA-Tencor™ FX200 metrology tool (KLA Tencor, Milpitas, Calif.)using a 49 point spiral scan with a 3 mm edge exclusion. Furtherpolishing details are set forth in Table B, below.

TABLE B Polishing Parameters Pads P1: VP6000 2 mm (0.080) SIV 508 mm(20″); D18AR; SG 0.8 P2: IC1010 2 mm (0.080) SIV 508 mm (20″); 1010; SG0.8 Slurry P1: ceria Slurry E (1:3) P2: Silica STI formulationsPolishing 20.7 kPa (3 psi), 93/87 rpm, 150 mL/min Process Polishing ToolApplied Materials Mirra ™ Thin Film KLA-Tencor ™ FX200, 49 point spiralscan w/ 3 mm Metrology edge exclusion Break-in Recipe P1: 3.17 kg (7lbf) for 40 min P2: 3.17 kg (7 lbf) for 40 min Conditioning P1: 100% insitu at 3.17 kg (7 lbf) P2: 100% in situ at 3.17 kg (7 lbf) Slurry DropPoint ~9.53 cm (~3.75″) from pad center

Polishing was continued for the indicated time intervals or to theextent of the indicated overpolish amount. In each of Tables 3, 4, and5, below, Performance Criterion A is trench oxide loss (Å): Acceptabletrench oxide loss is less than 250 Å at a 500 Å overpolish amount,preferably, less than 215 Å at 500 Å overpolish amount; PerformanceCriterion B is SiN loss (Å): Acceptable SiN loss is less than 200 Å at a500 Å overpolish amount, preferably, less than 150 Å at a 500 Åoverpolish amount; and Performance Criterion A is dishing (Å):Acceptable dishing is less than 200 Å at 500 Å overpolish amount,preferably, less than 175 Å at 500 Å overpolish amount.

Where otherwise indicated, the polished substrate was a recycledtetraethoxylsilicate (TEOS) wafer (TENR) used for blanket wafer studies.

TABLE 1 Slurry Formulation Details Slurry/ Amount pH (wt. % Copolymer(adjusted with Slurry solids) (ppm) HNO₃) 1* A/1 none 3.3 2 A/3 10 ppmof 3.3 copolymer 1 3 A/3 20 ppm of 3.3 copolymer 2 *Denotes ComparativeExample.

Example: Polishing Results

Polishing was performed using the indicated slurries listed in Table 1,above, on an STI Wafer substrate having a 50% PD feature. Polishing wasconducted in multiple steps using the indicated slurry. Results areshown in Table 2, below. Performance Criterion A is trench oxide loss(Å); Performance Criterion B is SiN loss (Å); and Performance CriterionA is dishing (Å).

TABLE 2 Copolymer Performance Slurry 1* 2 3 Performance Parameter A B CA B C A B C Oxide 113 52 29 23 Overpolish 218 111 54 57 Amount, Å 274127 81 46 302 171 51 121 403 167 100 67 433 236 145 91 530 303 95 208587 307 195 112 727 359 208 150 730 280 156 124 804 446 147 299 1071 609208 401

As shown in Table 2, above, copolymer 1 provides excellent polishingperformance and improves all of trench oxide loss A, SiN loss B anddishing C versus the same slurry without the copolymer in ComparativeExample 1.

Compared to the composition of Comparative Example 1*, the compositionsof Examples 2 and 3 show better dishing and trench oxide loss.

We claim:
 1. An aqueous chemical mechanical planarization polishing composition comprising a dispersion of a plurality of cationic elongated colloidal silica particles which contain a cationic nitrogen atom with a dispersion of spherical colloidal silica particles, wherein colloidal silica particles have a weight average size of 25 nm to 80 nm, and from 10 to 20 ppm of a cationic copolymer of diallylammonium chloride and sulfur dioxide, a cationic copolymer of diallylmonomethylammonium chloride and sulfur dioxide, or mixtures thereof, wherein the cationic copolymers have a weight average molecular weight of 2000 to 12,000, and the compositions have a pH of 2.5 to 4 and, further wherein, the amount of the dispersion of the cationic elongated colloidal silica particles ranges from 1 to 25 wt %, all weights based on the total weight of the composition.
 2. The aqueous chemical mechanical planarization polishing composition as claimed in claim 1, wherein the dispersion of the cationic elongated colloidal silica particles has for the average particle an aspect ratio of longest dimension to the diameter which is perpendicular to the longest dimension of 1.8:1 to 3:1.
 3. The aqueous chemical mechanical planarization polishing composition as claimed in claim 1, comprising a mixture of a dispersion of the cationic elongated colloidal silica particles and a dispersion of spherical colloidal silica particles, wherein the amount of the dispersion of the cationic elongated colloidal silica particles ranges from 80 to 99.9 wt. %, based on the total solids weight of the colloidal silica particles in the composition.
 4. The chemical mechanical planarization polishing composition as claimed in claim 1, wherein the cationic copolymer of diallylammonium chloride and sulfur dioxide comprises 45 to 55 mole % of the diallylammonium chloride having a cationic amine group and 45 to 55 mole % of the sulfur dioxide.
 5. The chemical mechanical planarization polishing composition as claimed in claim 1, wherein the cationic copolymer of diallylmonomethylammonium chloride and sulfur dioxide comprises 45 to 55 mole % of the diallylmonomethylammonium chloride having a cationic amine group and 45 to 55 mole % of the sulfur dioxide.
 6. The chemical mechanical planarization polishing composition as claimed in claim 1, wherein the amount of the dispersion of the cationic elongated colloidal silica particles ranges from 1 to 20 wt %. 